Surface acoustic wave sensor for refrigerant leakage detection

Abstract

A SAW sensor is optimized for detection of refrigerant leakage in a refrigerant system or other gases, vapors, explosives or chemicals of interest. The SAW sensor includes a piezoelectric substrate; an interdigitated transducer deposited on the piezoelectric substrate, the interdigitated transducer having an input portion that receives input surface acoustic waves and an output portion that emits output surface acoustic waves; and a refrigerant sensor film located between the input portion and the output portion of the interdigitated transducer, the refrigerant sensor film including a sorbent material that is selected for preferential adsorption of a target refrigerant over atmospheric gases. Adsorption of the target refrigerant by the sorbent material results in a frequency shift of a frequency of the output surface acoustic waves relative to a frequency of the input surface acoustic waves. The sorbent material may be a metal organic framework (MOF) material, a covalent organic framework (COF) material, a porous organic cage or organic macrocyles such as calix [n] arene and its related derivatives.

What is claimed is: 
     
       1. A surface acoustic wave (SAW) sensor for sensing a refrigerant comprising:
 a piezoelectric substrate that is delineated into a reference channel and a refrigerant channel; 
 the reference channel comprising a first interdigitated transducer deposited on the piezoelectric substrate, the first interdigitated transducer having an input portion that receives input surface acoustic waves and an output portion that emits output surface acoustic waves; 
 the refrigerant channel comprising a second interdigitated transducer deposited on the piezoelectric substrate, the second interdigitated transducer having an input portion that receives input surface acoustic waves and an output portion that emits output surface acoustic waves; and a refrigerant sensor film located between the input portion and the output portion of the second interdigitated transducer, the refrigerant sensor film including a sorbent material that is selected for preferential adsorption of a target refrigerant over atmospheric gases; 
 wherein in the refrigerant channel adsorption of the target refrigerant by the sorbent material results in a frequency shift of a frequency of the output surface acoustic waves relative to a frequency of the input surface acoustic waves, and in the reference channel there is no frequency shift of a frequency of the output surface acoustic waves relative to a frequency of the input surface acoustic waves; 
 wherein the sorbent material is a metal organic framework (MOF) material that is generated from an organic building unit and a metal center including one of alkali, alkaline, transition, lanthanides and actinides with 2+, 3+ and 4+ oxidation number, and the organic building unit includes one of 1,4-beneze-dicarboxylate, 1,3-benzene-dicarboxylate, 1,2,4,5-beneze-tetracarboxylate, 1,3,5-benzene-tricarboxylate, 4,4′-sulfonyldibenzoate or an organic macrocycles; or 
 wherein the sorbent material is a covalent organic framework (COF) material. 
 
     
     
       2. The SAW sensor of  claim 1 , wherein each of the reference channel and the refrigerant channel further comprises an input refection grating that adds resonance to generate the input surface acoustic waves, and an output reflection grating that adds resonance to the output surface acoustic waves. 
     
     
       3. The SAW sensor of  claim 1 , further comprising a signal generator for generating an input signal to generate the input surface acoustic waves, and a signal processing unit that is configured to process the output surface acoustic waves, wherein the signal processing unit determines whether the target refrigerant is present at the SAW sensor based on a comparison of the frequency shift of the output surface acoustic waves relative to the input surface acoustic waves in the refrigerant channel and a frequency of the output surface acoustic waves from the reference channel. 
     
     
       4. A method of detecting a target refrigerant comprising the steps of:
 inputting an input signal to a surface acoustic wave (SAW) sensor to generate input surface acoustic waves; 
 propagating the input surface acoustic waves through a refrigerant sensor film of the SAW sensor to generate output surface acoustic waves, wherein the refrigerant sensor film includes a sorbent material that is selected for preferential adsorption of the target refrigerant over atmospheric gases; 
 measuring the output surface acoustic waves and a calculating a frequency shift of a frequency of the output surface acoustic waves relative to a frequency of the input surface acoustic waves; and 
 determining a concentration of the target refrigerant based on the frequency shift; 
 wherein the sorbent material is a metal organic framework (MOF) material that is generated from an organic building unit and a metal center including one of alkali, alkaline, transition, lanthanides and actinides with 2+, 3+ and 4+ oxidation number, and the organic building unit includes one of 1,4-beneze-dicarboxylate, 1,3-benzene-dicarboxylate, 1,2,4,5-beneze-tetracarboxylate, 1,3,5-benzene-tricarboxylate, 4,4′-sulfonyldibenzoate or an organic macrocycles; or the sorbent material is a covalent organic framework (COF) material; and 
 wherein the SAW sensor comprises a refrigerant channel that includes the refrigerant sensor film and a reference channel that does not include a refrigerant sensor film, the method further comprising: 
 propagating the input surface acoustic waves through the reference channel to generate output surface acoustic waves from the reference channel; 
 measuring the output surface acoustic waves from the reference channel; and 
 determining the concentration of the target refrigerant based on a comparison of the frequency shift of the output surface acoustic waves relative to the input surface acoustic waves in the refrigerant channel and a frequency of the output surface acoustic waves from the reference channel. 
 
     
     
       5. The method of detecting a target refrigerant of  claim 4 , wherein the target refrigerant is a class A2L or class A3 refrigerant. 
     
     
       6. The method of detecting a target refrigerant of  claim 4 , wherein the target refrigerant is an R32 refrigerant. 
     
     
       7. The method of detecting a target refrigerant of  claim 4 , further comprising optimizing at least one of a pore size and thickness of the refrigerant sensor film for detecting one or more specific target refrigerants. 
     
     
       8. A method of detecting a target refrigerant comprising the steps of:
 inputting an input signal to a surface acoustic wave (SAW) sensor to generate input surface acoustic waves; 
 propagating the input surface acoustic waves through a refrigerant sensor film of the SAW sensor to generate output surface acoustic waves, wherein the refrigerant sensor film includes a sorbent material that is selected for preferential adsorption of the target refrigerant over atmospheric gases; 
 measuring the output surface acoustic waves and a calculating a frequency shift of a frequency of the output surface acoustic waves relative to a frequency of the input surface acoustic waves; 
 determining a concentration of the target refrigerant based on the frequency shift; 
 wherein the sorbent material is a metal organic framework (MOF) material that is generated from an organic building unit and a metal center including one of alkali, alkaline, transition, lanthanides and actinides with 2+, 3+ and 4+ oxidation number, and the organic building unit includes one of 1,4-beneze-dicarboxylate, 1,3-benzene-dicarboxylate, 1,2,4,5-beneze-tetracarboxylate, 1,3,5-benzene-tricarboxylate, 4,4′-sulfonyldibenzoate or an organic macrocycles; or the sorbent material is a covalent organic framework (COF) material; and 
 optimizing at least one of a pore size and thickness of the refrigerant sensor film for detecting one or more specific target refrigerants.